DESCRIPTION (provided by candidate): All organisms display daily cyclical changes known as circadian rhythms in their physiological processes, and in mammals such rhythms are driven internally by the suprachiasmatic nucleus (SCN). These internal rhythms are reset ("entrained") daily by the solar cycle so that they are in phase with the external light/dark cycle. Desynchronization between the internal and external rhythms results in "jet lag" symptoms which can have serious health consequences. Besides the classical photoreceptors, that is, rods and cones, the recently identified intrinsically photosensitive retinal ganglion cells (ipRGCs) are also involved in entrainment. While the rods/cones and the ipRGCs are known to be physiologically distinct, their differential roles in entrainment are poorly understood. In addition, interactions between the rod/cone system and the ipRGCs have not been explored. In this project, both issues will be studied at the retinal and the SCN levels, using patch-clamp and extracellular recording techniques combined with pharmacological manipulations. These experiments may enable a better understanding of how the mammalian circadian pacemaker is regulated, which in turn may lead to better therapies and workplace policies combating/preventing jet lag problems.